1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition and a piezoelectric ceramic element using the same. The present invention particularly relates to a piezoelectric ceramic composition to be used for materials for, for example, piezoelectric ceramic filters, piezoelectric oscillators and piezoelectric vibrators, and a piezoelectric ceramic element using the same.
2. Description of the Related Art
Piezoelectric ceramic compositions containing, for example, lead zirconate titanate (Pb(TixZr1xe2x88x92x)O3) or lead titanate (PbTiO3) as a principal component have been widely used for piezoelectric ceramic compositions intended for use in piezoelectric ceramic elements such as piezoelectric ceramic filters, piezoelectric ceramic oscillators and piezoelectric ceramic vibrators.
Lead oxide is usually used in the manufacturing process of the piezoelectric ceramic composition mainly composed of lead titanate zirconate and lead titanate. Consequently, facilities such as a filter for removing lead dusts should be provided in order to prevent pollution caused by evaporation of lead oxide, thus resulting in a high production cost. Uniformity of the product is also decreased due to evaporation of lead oxide.
For solving the problems as described above, piezoelectric ceramic compositions mainly composed of layered bismuth compounds such as (Ca1xe2x88x92xMx)Bi4Ti4O15, or compounds prepared by adding Mn therein, have been used. Such piezoelectric ceramic composition do not cause the troubles described above since they do not contain any lead oxide.
However, the conventional piezoelectric ceramic composition mainly composed of (Ca1xe2x88x92xMx)Bi4Ti4O15 needs to be fired at a temperature as high as 1150xc2x0 C. or above in order to obtain a ceramic exhibiting an electromechanical coupling coefficient kt high enough for practical uses (10% or more). Accordingly, an electrode material having a higher melting point than the firing temperature needs to be used for piezoelectric ceramic elements comprising inner electrodes, forcing the use of expensive materials such as platinum and palladium. It is a problem that the production cost of the piezoelectric ceramic element is increased by using such expensive electrode materials.
Accordingly, the main object of the present invention is to provide a piezoelectric ceramic composition that can be fired at a temperature as low as 1100xc2x0 C. or below besides being able to obtain a piezoelectric ceramic that exhibits an electromechanical coupling coefficient kt of the order sufficient for practical uses, and a piezoelectric ceramic element using the piezoelectric ceramic composition.
In one aspect, the present invention provides a piezoelectric ceramic composition containing a principal component represented by a general formula of CaBi4(Ti1xe2x88x92ySiy)4O16, wherein y is within the range of 0 less than yxe2x89xa60.5.
The present invention also provides a piezoelectric ceramic composition containing a principal component represented by a general formula of (Ca1xe2x88x92xMx)Bi4((Ti1xe2x88x92ySiy)4O15 in which M is Mxe2x80x2 or Mxe2x80x3, wherein Mxe2x80x2 is a divalent metallic element other than Ca and Mxe2x80x3 is a trivalent metallic element other than Bi, and wherein y is within the range of 0 less than yxe2x89xa60.5 and 0 less than xxe2x89xa60.5.
Preferably, x is within the range of 0 less than xxe2x89xa60.5 when M in the principal component is Mxe2x80x2, a divalent metallic element, and x is within the range of 0 less than xxe2x89xa60.3 when M is Mxe2x80x3, a trivalent metallic element in the piezoelectric ceramic composition containing the divalent or trivalent metallic element M.
It is also preferable that M in the principal component is at least one of the elements Mg, Sr, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y in the piezoelectric ceramic composition containing the divalent or trivalent metallic element M.
The present invention also provides a piezoelectric ceramic composition containing a principal component represented by a general formula of (Ca1xe2x88x92xMxe2x80x32x/3)Bi4(Ti1xe2x88x92ySiy)4O15 in which Mxe2x80x3 represents the trivalent metallic element other than Bi, wherein x is within the range of 0 less than xxe2x89xa60.45 and y is within the range of 0 less than yxe2x89xa60.5.
It is preferable that Mxe2x80x3 in the principal component is at least one of the elements La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y in the piezoelectric ceramic composition containing the trivalent metallic element Mxe2x80x3.
The present invention also provides a piezoelectric ceramic composition comprising a principal component represented by a general formula of CaBi4Ti4O15, containing about 0.5 mol or less (excluding zero) of Si relative to 1 mol of Bi in the principal component represented by the general formula described above, and containing about 0.125 mol or less (excluding zero) of a divalent metallic element other than Ca relative to 1 mol of Bi in the principal component represented by the general formula as described above, or about 0.075 mol or less (excluding zero) of a trivalent metallic element other than Bi relative to 1 mol of Bi in the principal component represented by the general formula as described above.
In the piezoelectric ceramic composition containing the divalent metallic element or the trivalent metallic element, these metallic elements are preferably at least one of the elements Mg, Sr, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
The piezoelectric ceramic composition may contain about 5.0% by weight or less of manganese calculated as MnCO3 relative to 100% parts by weight of the principal component.
The present invention also provides a piezoelectric ceramic element comprising electrodes formed on the piezoelectric ceramic using any one of the piezoelectric ceramic compositions as described above.
A piezoelectric ceramic having an electromechanical coupling coefficient of 10% or more can be obtained by firing the piezoelectric ceramic composition as described above at a temperature of 1100xc2x0 C. or below.
The piezoelectric ceramic element, in which electrodes are formed on the piezoelectric ceramic using the piezoelectric ceramic composition as hitherto described, has good electric characteristics while enabling the production cost to be reduced.
These and other objects, features and advantages of the present invention as hitherto described will be made more obvious from the detailed descriptions of the embodiments according to the present invention with reference to the attached drawings.